I am so very sorry for your sad loss!
It is one thing for a senior citizen to die but it is even sadder when a pet dies in the prime of his life.
I think that since your dog had seizures from a young age he may have had a malformation in his brain. Epilepsy can also result from trauma to the head. I assume that your dog did not have head trauma. There is a saying in veterinary medicine that congenital abnormalities run in threes. Your dog may have had other congenital problems that were latent, or subtle, so they went undiagnosed. Seizures can put great stress on the body, especially if under-controlled or uncontrolled. They put strain on the heart, cause fatal hyperthermia, and further brain damage. If your dog already had a undiagnosed heart condition or other brain damage his last seizure may have just put his weakened body over the edge.
This of course is just speculation. The only definitive method to diagnose the cause of death would be a post-mortem with blood screens.
Thank you so much Dr.Cheng.Since I had taken him to an emergency animal clinic and not his regular vet I couldnt get an answer right away.Your answer explains alot and has made me feel better in that I did all that I can do. Now I have to wait and let time heal my heart.Thank You agian I appreciate it!